Informations : A report, "Viking relativity experiment: verification of signal retardation by solar gravity" published in 1979 by researchers at MIT and the Jet Propulsion Laboratory, analyzed 14 months of data obtained from radio ranging to Viking to verify the prediction of the general theory of relativity. The round-trip or echo delays of light signals traveling between the Earth and Mars would be increased by the direct effect of solar gravity. The theory included gravitational time dilation, where time passes differently in regions of different gravitational potential.